A useful class of positive-working photoresist compositions comprises a polymer containing recurring groups with pendant quinone diazide groups that are light sensitive, and a photoactive dissolution inhibitor monomer that tends to crosslink the polymer by heat in areas wherein the quinone diazide has not been decomposed by exposure to activating radiation. One of the monomer's functions is to convert to a ketene that causes crosslinking, thereby providing thermal resistance, as is well known. Examples are described in U.S. Pat. No. 4,365,019, wherein the monomer comprises, e.g., 1,3,5-trihydroxybenzene esterified with 1,2-naphthoquinone diazide sulfonic acid.
Such resists have usually functioned very well. However, under certain conditions, such resist compositions have occasionally exhibited a tendency to crystallize out of solution, rendering it impossible to coat them into a layered format suitable for use as a resist on a substrate. There has been a need, therefore, prior to this invention, to find a modification that will keep the resist composition in solution for purposes of coating.